--[[

Here is a MQTT v3.1.1 protocol implementation

MQTT v3.1.1 documentation (DOC):
	http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/errata01/os/mqtt-v3.1.1-errata01-os-complete.html

]]

-- module table
local protocol4 = {}

-- load required stuff
local type = type
local error = error
local assert = assert
local require = require
local tostring = tostring
local setmetatable = setmetatable

local const = require("mqtt.const")
local const_v311 = const.v311

local protocol = require("mqtt.protocol")
local make_uint8 = protocol.make_uint8
local make_uint16 = protocol.make_uint16
local make_string = protocol.make_string
local make_header = protocol.make_header
local check_qos = protocol.check_qos
local check_packet_id = protocol.check_packet_id
local combine = protocol.combine
local packet_type = protocol.packet_type
local packet_mt = protocol.packet_mt
local connack_packet_mt = protocol.connack_packet_mt
local start_parse_packet = protocol.start_parse_packet
local parse_packet_connect_input = protocol.parse_packet_connect_input
local parse_string = protocol.parse_string
local parse_uint8 = protocol.parse_uint8
local parse_uint16 = protocol.parse_uint16

-- Create Connect Flags data, DOC: 3.1.2.3 Connect Flags
local function make_connect_flags(args)
	local byte = 0 -- bit 0 should be zero
	-- DOC: 3.1.2.4 Clean Session
	if args.clean ~= nil then
		assert(type(args.clean) == "boolean", "expecting .clean to be a boolean")
		if args.clean then
			byte = byte | (1 << 1)
		end
	end
	-- DOC: 3.1.2.5 Will Flag
	if args.will ~= nil then
		-- check required args are presented
		assert(type(args.will) == "table", "expecting .will to be a table")
		assert(type(args.will.payload) == "string", "expecting .will.payload to be a string")
		assert(type(args.will.topic) == "string", "expecting .will.topic to be a string")
		if args.will.qos ~= nil then
			assert(type(args.will.qos) == "number", "expecting .will.qos to be a number")
			assert(check_qos(args.will.qos), "expecting .will.qos to be a valid QoS value")
		end
		if args.will.retain ~= nil then
			assert(type(args.will.retain) == "boolean", "expecting .will.retain to be a boolean")
		end
		-- will flag should be set to 1
		byte = byte | ( 1 << 2 )
		-- DOC: 3.1.2.6 Will QoS
		byte = byte | ((args.will.qos or 0) << 3)
		-- DOC: 3.1.2.7 Will Retain
		if args.will.retain then
			byte = byte | (1 << 5)
		end
	end
	-- DOC: 3.1.2.8 User Name Flag
	if args.username ~= nil then
		assert(type(args.username) == "string", "expecting .username to be a string")
		byte = byte | ( 1 << 7 )
	end
	-- DOC: 3.1.2.9 Password Flag
	if args.password ~= nil then
		assert(type(args.password) == "string", "expecting .password to be a string")
		assert(args.username, "the .username is required to set .password")
		byte = byte | (1 << 6)
	end
	return make_uint8(byte)
end

-- Create CONNECT packet, DOC: 3.1 CONNECT – Client requests a connection to a Server
local function make_packet_connect(args)
	-- check args
	assert(type(args.id) == "string", "expecting .id to be a string with MQTT client id")
	-- DOC: 3.1.2.10 Keep Alive
	local keep_alive_ival = 0
	if args.keep_alive then
		assert(type(args.keep_alive) == "number")
		keep_alive_ival = args.keep_alive
	end
	-- DOC: 3.1.2 Variable header
	local variable_header = combine(
		make_string("MQTT"), 				-- DOC: 3.1.2.1 Protocol Name
		make_uint8(4), 						-- DOC: 3.1.2.2 Protocol Level (4 is for MQTT v3.1.1)
		make_connect_flags(args), 			-- DOC: 3.1.2.3 Connect Flags
		make_uint16(keep_alive_ival) 		-- DOC: 3.1.2.10 Keep Alive
	)
	-- DOC: 3.1.3 Payload
	-- DOC: 3.1.3.1 Client Identifier
	local payload = combine(
		make_string(args.id)
	)
	if args.will then
		-- DOC: 3.1.3.2 Will Topic
		assert(type(args.will.topic) == "string", "expecting will.topic to be a string")
		payload:append(make_string(args.will.topic))
		-- DOC: 3.1.3.3 Will Message
		assert(args.will.payload == nil or type(args.will.payload) == "string", "expecting will.payload to be a string or nil")
		payload:append(make_string(args.will.payload or ""))
	end
	if args.username then
		-- DOC: 3.1.3.4 User Name
		payload:append(make_string(args.username))
		if args.password then
			-- DOC: 3.1.3.5 Password
			payload:append(make_string(args.password))
		end
	end
	-- DOC: 3.1.1 Fixed header
	local header = make_header(packet_type.CONNECT, 0, variable_header:len() + payload:len())
	return combine(header, variable_header, payload)
end

-- Create CONNACK packet, DOC: 3.2 CONNACK – Acknowledge connection request
local function make_packet_connack(args)
	-- check args
	assert(type(args.sp) == "boolean", "expecting .sp to be a boolean")
	assert(type(args.rc) == "number", "expecting .rc to be a boolean")
	-- DOC: 3.2.2.1 Connect Acknowledge Flags
	-- DOC: 3.2.2.2 Session Present
	local byte1
	if args.sp then
		byte1 = 1 -- bit 0 of the Connect Acknowledge Flags.
	else
		byte1 = 0
	end
	-- DOC: 3.2.2.3 Connect Return code
	local byte2 = args.rc
	-- DOC: 3.2.2 Variable header
	local variable_header = combine(
		make_uint8(byte1),
		make_uint8(byte2)
	)
	-- DOC: 3.2.1 Fixed header
	local header = make_header(packet_type.CONNACK, 0, variable_header:len()) -- NOTE: fixed flags value 0x0
	return combine(header, variable_header)
end

-- Create PUBLISH packet, DOC: 3.3 PUBLISH – Publish message
local function make_packet_publish(args)
	-- check args
	assert(type(args.topic) == "string", "expecting .topic to be a string")
	if args.payload ~= nil then
		assert(type(args.payload) == "string", "expecting .payload to be a string")
	end
	if args.qos ~= nil then
		assert(type(args.qos) == "number", "expecting .qos to be a number")
		assert(check_qos(args.qos), "expecting .qos to be a valid QoS value")
	end
	if args.retain ~= nil then
		assert(type(args.retain) == "boolean", "expecting .retain to be a boolean")
	end
	if args.dup ~= nil then
		assert(type(args.dup) == "boolean", "expecting .dup to be a boolean")
	end
	-- DOC: 3.3.1 Fixed header
	local flags = 0
	-- 3.3.1.3 RETAIN
	if args.retain then
		flags = flags | 0x1
	end
	-- DOC: 3.3.1.2 QoS
	flags = flags | ((args.qos or 0) << 1)
	-- DOC: 3.3.1.1 DUP
	if args.dup then
		flags = flags | (1 << 3)
	end
	-- DOC: 3.3.2  Variable header
	local variable_header = combine(
		make_string(args.topic)
	)
	-- DOC: 3.3.2.2 Packet Identifier
	if args.qos and args.qos > 0 then
		assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
		assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
		variable_header:append(make_uint16(args.packet_id))
	end
	local payload
	if args.payload then
		payload = args.payload
	else
		payload = ""
	end
	-- DOC: 3.3.1 Fixed header
	local header = make_header(packet_type.PUBLISH, flags, variable_header:len() + payload:len())
	return combine(header, variable_header, payload)
end

-- Create PUBACK packet, DOC: 3.4 PUBACK – Publish acknowledgement
local function make_packet_puback(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	-- DOC: 3.4.1 Fixed header
	local header = make_header(packet_type.PUBACK, 0, 2)
	-- DOC: 3.4.2 Variable header
	local variable_header = make_uint16(args.packet_id)
	return combine(header, variable_header)
end

-- Create PUBREC packet, DOC: 3.5 PUBREC – Publish received (QoS 2 publish received, part 1)
local function make_packet_pubrec(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	-- DOC: 3.5.1 Fixed header
	local header = make_header(packet_type.PUBREC, 0, 2)
	-- DOC: 3.5.2 Variable header
	local variable_header = make_uint16(args.packet_id)
	return combine(header, variable_header)
end

-- Create PUBREL packet, DOC: 3.6 PUBREL – Publish release (QoS 2 publish received, part 2)
local function make_packet_pubrel(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	-- DOC: 3.6.1 Fixed header
	local header = make_header(packet_type.PUBREL, 0x2, 2) -- flags are 0x2 == 0010 bits (fixed value)
	-- DOC: 3.6.2 Variable header
	local variable_header = make_uint16(args.packet_id)
	return combine(header, variable_header)
end

-- Create PUBCOMP packet, DOC: 3.7 PUBCOMP – Publish complete (QoS 2 publish received, part 3)
local function make_packet_pubcomp(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	-- DOC: 3.7.1 Fixed header
	local header = make_header(packet_type.PUBCOMP, 0, 2)
	-- DOC: 3.7.2 Variable header
	local variable_header = make_uint16(args.packet_id)
	return combine(header, variable_header)
end

-- Create SUBSCRIBE packet, DOC: 3.8 SUBSCRIBE - Subscribe to topics
local function make_packet_subscribe(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	assert(type(args.subscriptions) == "table", "expecting .subscriptions to be a table")
	assert(#args.subscriptions > 0, "expecting .subscriptions to be a non-empty array")
	-- DOC: 3.8.2 Variable header
	local variable_header = combine(
		make_uint16(args.packet_id)
	)
	-- DOC: 3.8.3 Payload
	local payload = combine()
	for i, subscription in ipairs(args.subscriptions) do
		assert(type(subscription) == "table", "expecting .subscriptions["..i.."] to be a table")
		assert(type(subscription.topic) == "string", "expecting .subscriptions["..i.."].topic to be a string")
		if subscription.qos ~= nil then
			assert(type(subscription.qos) == "number", "expecting .subscriptions["..i.."].qos to be a number")
			assert(check_qos(subscription.qos), "expecting .subscriptions["..i.."].qos to be a valid QoS value")
		end
		payload:append(make_string(subscription.topic))
		payload:append(make_uint8(subscription.qos or 0))
	end
	-- DOC: 3.8.1 Fixed header
	local header = make_header(packet_type.SUBSCRIBE, 2, variable_header:len() + payload:len()) -- NOTE: fixed flags value 0x2
	return combine(header, variable_header, payload)
end

-- Create SUBACK packet, DOC: 3.9 SUBACK – Subscribe acknowledgement
local function make_packet_suback(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	assert(type(args.rc) == "table", "expecting .rc to be a table")
	assert(#args.rc > 0, "expecting .rc to be a non-empty array")
	-- DOC: 3.9.2 Variable header
	local variable_header = combine(
		make_uint16(args.packet_id)
	)
	-- DOC: 3.9.3 Payload
	local payload = combine()
	for i, rc in ipairs(args.rc) do
		assert(type(rc) == "number", "expecting .rc["..i.."] to be a number")
		assert(rc >= 0 and rc <= 255, "expecting .rc["..i.."] to be in range [0, 255]")
		payload:append(make_uint8(rc))
	end
	-- DOC: 3.9.1 Fixed header
	local header = make_header(packet_type.SUBACK, 0, variable_header:len() + payload:len()) -- NOTE: fixed flags value 0x0
	return combine(header, variable_header, payload)
end

-- Create UNSUBSCRIBE packet, DOC: 3.10 UNSUBSCRIBE – Unsubscribe from topics
local function make_packet_unsubscribe(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	assert(type(args.subscriptions) == "table", "expecting .subscriptions to be a table")
	assert(#args.subscriptions > 0, "expecting .subscriptions to be a non-empty array")
	-- DOC: 3.10.2 Variable header
	local variable_header = combine(
		make_uint16(args.packet_id)
	)
	-- DOC: 3.10.3 Payload
	local payload = combine()
	for i, subscription in ipairs(args.subscriptions) do
		assert(type(subscription) == "string", "expecting .subscriptions["..i.."] to be a string")
		payload:append(make_string(subscription))
	end
	-- DOC: 3.10.1 Fixed header
	local header = make_header(packet_type.UNSUBSCRIBE, 2, variable_header:len() + payload:len()) -- NOTE: fixed flags value 0x2
	return combine(header, variable_header, payload)
end

-- Create UNSUBACK packet, DOC: 3.11 UNSUBACK – Unsubscribe acknowledgement
local function make_packet_unsuback(args)
	-- check args
	assert(type(args.packet_id) == "number", "expecting .packet_id to be a number")
	assert(check_packet_id(args.packet_id), "expecting .packet_id to be a valid Packet Identifier")
	-- DOC: 3.11.2 Variable header
	local variable_header = combine(
		make_uint16(args.packet_id)
	)
	-- DOC: 3.11.3 Payload
	-- The UNSUBACK Packet has no payload.
	-- DOC: 3.11.1 Fixed header
	local header = make_header(packet_type.UNSUBACK, 0, variable_header:len()) -- NOTE: fixed flags value 0x0
	return combine(header, variable_header)
end

-- Create packet of given {type: number} in args
function protocol4.make_packet(args)
	assert(type(args) == "table", "expecting args to be a table")
	assert(type(args.type) == "number", "expecting .type number in args")
	local ptype = args.type
	if ptype == packet_type.CONNECT then			-- 1
		return make_packet_connect(args)
	elseif ptype == packet_type.CONNACK then		-- 2
		return make_packet_connack(args)
	elseif ptype == packet_type.PUBLISH then		-- 3
		return make_packet_publish(args)
	elseif ptype == packet_type.PUBACK then			-- 4
		return make_packet_puback(args)
	elseif ptype == packet_type.PUBREC then			-- 5
		return make_packet_pubrec(args)
	elseif ptype == packet_type.PUBREL then			-- 6
		return make_packet_pubrel(args)
	elseif ptype == packet_type.PUBCOMP then		-- 7
		return make_packet_pubcomp(args)
	elseif ptype == packet_type.SUBSCRIBE then		-- 8
		return make_packet_subscribe(args)
	elseif ptype == packet_type.SUBACK then			-- 9
		return make_packet_suback(args)
	elseif ptype == packet_type.UNSUBSCRIBE then	-- 10
		return make_packet_unsubscribe(args)
	elseif ptype == packet_type.UNSUBACK then		-- 11
		return make_packet_unsuback(args)
	elseif ptype == packet_type.PINGREQ then		-- 12
		-- DOC: 3.12 PINGREQ – PING request
		return combine("\192\000") -- 192 == 0xC0, type == 12, flags == 0
	elseif ptype == packet_type.PINGRESP then		-- 13
		-- DOC: 3.13 PINGRESP – PING response
		return combine("\208\000") -- 208 == 0xD0, type == 13, flags == 0
	elseif ptype == packet_type.DISCONNECT then		-- 14
		-- DOC: 3.14 DISCONNECT – Disconnect notification
		return combine("\224\000") -- 224 == 0xD0, type == 14, flags == 0
	else
		error("unexpected protocol4 packet type to make: "..ptype)
	end
end

-- Parse CONNACK packet, DOC: 3.2 CONNACK – Acknowledge connection request
local function parse_packet_connack(ptype, flags, input)
	-- DOC: 3.2.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	local byte1, byte2 = parse_uint8(input.read_func), parse_uint8(input.read_func)
	local sp = (byte1 & 0x1) ~= 0
	return setmetatable({type=ptype, sp=sp, rc=byte2}, connack_packet_mt)
end

-- Parse PUBLISH packet, DOC: 3.3 PUBLISH – Publish message
local function parse_packet_publish(ptype, flags, input)
	-- DOC: 3.3.1.1 DUP
	local dup = (flags & 0x8) ~= 0
	-- DOC: 3.3.1.2 QoS
	local qos = (flags >> 1) & 0x3
	-- DOC: 3.3.1.3 RETAIN
	local retain = (flags & 0x1) ~= 0
	-- DOC: 3.3.2.1 Topic Name
	if input.available < 2 then
		return false, packet_type[ptype]..": expecting data of length at least 2 bytes"
	end
	local topic_len = parse_uint16(input.read_func)
	if input.available < topic_len then
		return false, packet_type[ptype]..": malformed packet: not enough data to parse topic"
	end
	local topic = input.read_func(topic_len)
	-- DOC: 3.3.2.2 Packet Identifier
	local packet_id
	if qos > 0 then
		-- DOC: 3.3.2.2 Packet Identifier
		if input.available < 2 then
			return false, packet_type[ptype]..": malformed packet: not enough data to parse packet_id"
		end
		packet_id = parse_uint16(input.read_func)
	end
	-- DOC: 3.3.3 Payload
	local payload
	if input.available > 0 then
		payload = input.read_func(input.available)
	end
	return setmetatable({type=ptype, dup=dup, qos=qos, retain=retain, packet_id=packet_id, topic=topic, payload=payload}, packet_mt)
end

-- Parse PUBACK packet, DOC: 3.4 PUBACK – Publish acknowledgement
local function parse_packet_puback(ptype, flags, input)
	-- DOC: 3.4.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	-- DOC: 3.4.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	return setmetatable({type=ptype, packet_id=packet_id}, packet_mt)
end

-- Parse PUBREC packet, DOC: 3.5 PUBREC – Publish received (QoS 2 publish received, part 1)
local function parse_packet_pubrec(ptype, flags, input)
	-- DOC: 3.4.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	-- DOC: 3.5.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	return setmetatable({type=ptype, packet_id=packet_id}, packet_mt)
end

-- Parse PUBREL packet, DOC: 3.6 PUBREL – Publish release (QoS 2 publish received, part 2)
local function parse_packet_pubrel(ptype, flags, input)
	if flags ~= 2 then
		-- DOC: The Server MUST treat any other value as malformed and close the Network Connection [MQTT-3.6.1-1].
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	-- DOC: 3.6.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	return setmetatable({type=ptype, packet_id=packet_id}, packet_mt)
end

-- Parse PUBCOMP packet, DOC: 3.7 PUBCOMP – Publish complete (QoS 2 publish received, part 3)
local function parse_packet_pubcomp(ptype, flags, input)
	-- DOC: 3.7.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	-- DOC: 3.7.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	return setmetatable({type=ptype, packet_id=packet_id}, packet_mt)
end

-- Parse SUBSCRIBE packet, DOC: 3.8 SUBSCRIBE - Subscribe to topics
local function parse_packet_subscribe(ptype, flags, input)
	if flags ~= 2 then
		-- DOC: The Server MUST treat any other value as malformed and close the Network Connection [MQTT-3.8.1-1].
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available < 5 then -- variable header (2) + payload: topic length (2) + qos (1)
		-- DOC: The payload of a SUBSCRIBE packet MUST contain at least one Topic Filter / QoS pair. A SUBSCRIBE packet with no payload is a protocol violation [MQTT-3.8.3-3]
		return false, packet_type[ptype]..": expecting data of length 5 bytes at least"
	end
	-- DOC: 3.8.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	-- DOC: 3.8.3 Payload
	local subscriptions = {}
	while input.available > 0 do
		local topic_filter, qos, err
		topic_filter, err = parse_string(input.read_func)
		if not topic_filter then
			return false, packet_type[ptype]..": failed to parse topic filter: "..err
		end
		qos, err = parse_uint8(input.read_func)
		if not qos then
			return false, packet_type[ptype]..": failed to parse qos: "..err
		end
		subscriptions[#subscriptions + 1] = {
			topic = topic_filter,
			qos = qos,
		}
	end
	return setmetatable({type=ptype, packet_id=packet_id, subscriptions=subscriptions}, packet_mt)
end

-- SUBACK return codes
-- DOC: 3.9.3 Payload
local suback_rc = {
	[0x00] = "Success - Maximum QoS 0",
	[0x01] = "Success - Maximum QoS 1",
	[0x02] = "Success - Maximum QoS 2",
	[0x80] = "Failure",
}
protocol4.suback_rc = suback_rc

--- Parsed SUBACK packet metatable
local suback_packet_mt = {
	__tostring = protocol.packet_tostring, -- packet-to-human-readable-string conversion metamethod using protocol.packet_tostring()
	reason_strings = function(self) -- Returns return codes descriptions for the SUBACK packet according to its rc field
		local human_readable = {}
		for i, rc in ipairs(self.rc) do
			local return_code = suback_rc[rc]
			if return_code then
				human_readable[i] = return_code
			else
				human_readable[i] = "Unknown: "..tostring(rc)
			end
		end
		return human_readable
	end,
}
suback_packet_mt.__index = suback_packet_mt
protocol4.suback_packet_mt = suback_packet_mt

-- Parse SUBACK packet, DOC: 3.9 SUBACK – Subscribe acknowledgement
local function parse_packet_suback(ptype, flags, input)
	-- DOC: 3.9.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available < 3 then
		return false, packet_type[ptype]..": expecting data of length at least 3 bytes"
	end
	-- DOC: 3.9.2 Variable header
	-- DOC: 3.9.3 Payload
	local packet_id = parse_uint16(input.read_func)
	local rc = {} -- DOC: The payload contains a list of return codes.
	while input.available > 0 do
		rc[#rc + 1] = parse_uint8(input.read_func)
	end
	return setmetatable({type=ptype, packet_id=packet_id, rc=rc}, suback_packet_mt)
end

-- Parse UNSUBSCRIBE packet, DOC: 3.10 UNSUBSCRIBE – Unsubscribe from topics
local function parse_packet_unsubscribe(ptype, flags, input)
	-- DOC: 3.10.1 Fixed header
	if flags ~= 2 then
		-- DOC: The Server MUST treat any other value as malformed and close the Network Connection [MQTT-3.10.1-1].
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available < 4 then -- variable header (2) + payload: topic length (2)
		-- DOC: The Payload of an UNSUBSCRIBE packet MUST contain at least one Topic Filter. An UNSUBSCRIBE packet with no payload is a protocol violation [MQTT-3.10.3-2].
		return false, packet_type[ptype]..": expecting data of length at least 4 bytes"
	end
	-- DOC: 3.10.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	-- DOC: 3.10.3 Payload
	local subscriptions = {}
	while input.available > 0 do
		local topic_filter, err = parse_string(input.read_func)
		if not topic_filter then
			return false, packet_type[ptype]..": failed to parse topic filter: "..err
		end
		subscriptions[#subscriptions + 1] = topic_filter
	end
	return setmetatable({type=ptype, packet_id=packet_id, subscriptions=subscriptions}, packet_mt)
end

-- Parse UNSUBACK packet, DOC: 3.11 UNSUBACK – Unsubscribe acknowledgement
local function parse_packet_unsuback(ptype, flags, input)
	-- DOC: 3.11.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 2 then
		return false, packet_type[ptype]..": expecting data of length 2 bytes"
	end
	-- DOC: 3.11.2 Variable header
	local packet_id = parse_uint16(input.read_func)
	return setmetatable({type=ptype, packet_id=packet_id}, packet_mt)
end

-- Parse PINGREQ packet, DOC: 3.12 PINGREQ – PING request
local function parse_packet_pingreq(ptype, flags, input)
	-- DOC: 3.12.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 0 then
		return false, packet_type[ptype]..": expecting data of length 0 bytes"
	end
	return setmetatable({type=ptype}, packet_mt)
end

-- Parse PINGRESP packet, DOC: 3.13 PINGRESP – PING response
local function parse_packet_pingresp(ptype, flags, input)
	-- DOC: 3.13.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 0 then
		return false, packet_type[ptype]..": expecting data of length 0 bytes"
	end
	return setmetatable({type=ptype}, packet_mt)
end

-- Parse DISCONNECT packet, DOC: 3.14 DISCONNECT – Disconnect notification
local function parse_packet_disconnect(ptype, flags, input)
	-- DOC: 3.14.1 Fixed header
	if flags ~= 0 then -- Reserved
		return false, packet_type[ptype]..": unexpected flags value: "..flags
	end
	if input.available ~= 0 then
		return false, packet_type[ptype]..": expecting data of length 0 bytes"
	end
	return setmetatable({type=ptype}, packet_mt)
end

-- Parse packet using given read_func
-- Returns packet on success or false and error message on failure
function protocol4.parse_packet(read_func)
	local ptype, flags, input = start_parse_packet(read_func)
	if not ptype then
		return false, flags -- flags is error message in this case
	end
	-- parse read data according type in fixed header
	if ptype == packet_type.CONNECT then			-- 1
		return parse_packet_connect_input(input, const_v311)
	elseif ptype == packet_type.CONNACK then		-- 2
		return parse_packet_connack(ptype, flags, input)
	elseif ptype == packet_type.PUBLISH then		-- 3
		return parse_packet_publish(ptype, flags, input)
	elseif ptype == packet_type.PUBACK then			-- 4
		return parse_packet_puback(ptype, flags, input)
	elseif ptype == packet_type.PUBREC then			-- 5
		return parse_packet_pubrec(ptype, flags, input)
	elseif ptype == packet_type.PUBREL then			-- 6
		return parse_packet_pubrel(ptype, flags, input)
	elseif ptype == packet_type.PUBCOMP then		-- 7
		return parse_packet_pubcomp(ptype, flags, input)
	elseif ptype == packet_type.SUBSCRIBE then		-- 8
		return parse_packet_subscribe(ptype, flags, input)
	elseif ptype == packet_type.SUBACK then			-- 9
		return parse_packet_suback(ptype, flags, input)
	elseif ptype == packet_type.UNSUBSCRIBE then	-- 10
		return parse_packet_unsubscribe(ptype, flags, input)
	elseif ptype == packet_type.UNSUBACK then		-- 11
		return parse_packet_unsuback(ptype, flags, input)
	elseif ptype == packet_type.PINGREQ then		-- 12
		return parse_packet_pingreq(ptype, flags, input)
	elseif ptype == packet_type.PINGRESP then		-- 13
		return parse_packet_pingresp(ptype, flags, input)
	elseif ptype == packet_type.DISCONNECT then		-- 14
		return parse_packet_disconnect(ptype, flags, input)
	else
		return false, "unexpected packet type received: "..tostring(ptype)
	end
end

-- Continue parsing of the MQTT v3.1.1 CONNECT packet
-- Internally called from the protocol.parse_packet_connect_input() function
-- Returns packet on success or false and error message on failure
function protocol4._parse_packet_connect_continue(input, packet)
	-- DOC: 3.1.3 Payload
	-- These fields, if present, MUST appear in the order Client Identifier, Will Topic, Will Message, User Name, Password
	local read_func = input.read_func
	local client_id, err

	-- DOC: 3.1.3.1 Client Identifier
	client_id, err = parse_string(read_func)
	if not client_id then
		return false, "CONNECT: failed to parse client_id: "..err
	end
	packet.id = client_id

	local will = packet.will
	if will then
		-- 3.1.3.2 Will Topic
		local will_topic, will_payload
		will_topic, err = parse_string(read_func)
		if not will_topic then
			return false, "CONNECT: failed to parse will_topic: "..err
		end
		will.topic = will_topic

		-- DOC: 3.1.3.3 Will Message
		will_payload, err = parse_string(read_func)
		if not will_payload then
			return false, "CONNECT: failed to parse will_payload: "..err
		end
		will.payload = will_payload
	end

	if packet.username then
		-- DOC: 3.1.3.4 User Name
		local username
		username, err = parse_string(read_func)
		if not username then
			return false, "CONNECT: failed to parse username: "..err
		end
		packet.username = username
	else
		packet.username = nil
	end

	if packet.password then
		-- DOC: 3.1.3.5 Password
		if not packet.username then
			return false, "CONNECT: MQTT v3.1.1 does not allow providing password without username"
		end
		local password
		password, err = parse_string(read_func)
		if not password then
			return false, "CONNECT: failed to parse password: "..err
		end
		packet.password = password
	else
		packet.password = nil
	end

	return setmetatable(packet, packet_mt)
end

-- export module table
return protocol4

-- vim: ts=4 sts=4 sw=4 noet ft=lua
